The present invention relates to a rotational vibration testing device for testing the affect on selected devices of both rotary shock and rotary vibration.
It is desirable to test the resistance of certain portable devices to rotary shock and vibration, particularly devices with moving parts and small tolerances such as computer disk drives and the like. The analysis and testing of a disk drive system""s ability to withstand rotational shock and vibration while in operation has become increasingly important as the portability of computer systems increases. Under some circumstance, rotary shock can be far more destructive than pure translational shock along an X, Y or Z axis. In testing disk drives, it is important to have a system that eliminates z-axis acceleration which could induce false drive failures and that has the ability to test disk drives of various payloads.
Disk drive manufacturer""s increasingly perform testing to ensure that disk drives can withstand requisite levels of rotary shock and vibration. However, current conventional test systems have several drawbacks. For example, rotating tables found in the prior art tend to vibrate and/or precess upon application of a rotary shock to the outer circumference of the table. This vibrations and/or precession may result in a dampening of shock applied to the table.
Some pre-existing rotary shock testing devices utilize rotating tables mounted on bearing plates situated along the axis of rotation. These devices have the bearings located near the center of rotation and do not sufficiently control the z-axis acceleration, and the axis of rotation of these devices may be negatively affected by heavy payloads.
Another drawback of some current rotary shock testing systems relates to the uncontrolled variability of the shock delivery system. For example, many conventional rotary shock tables use a spring-based system for delivering the shock to the rotary table. The force applied by spring-based systems changes over the life of the spring. Other systems utilize pneumatic cylinders to impart a force on the system. However, the amount of force exerted onto the system varies with the varying gas pressure in the pneumatic cylinder and the position at which the cylinder piston strikes the unit.
What is needed is a rotary shock testing device that avoids the disadvantages of pre-existing rotary shock testing devices discussed above.
Accordingly, the present invention is a rotary test device for testing of both rotary shock and rotary vibration when used in conjunction with a 1200 lb force electrodynamic shaker that includes a hub with tapered annular roller bearings, in opposition, to support it between two compression rings. The compression rings are preloaded over the bearings to eliminate z-axis movement. A motion arm connects to a radial arm on the side of hub via flexible nylon or equivalent material. The other end of the motion arm mounts to a height adjuster, which bolts to the 1200 lb force electrodynamic shaker. When the motion arm moves fore and aft, the linear acceleration is converted to rotational acceleration based on the radius from the stinger to the center of rotation. The nylon or equivalent material median between the motion arm and the hub allows for sufficient rotational flex without fore and aft play. The large tapered annular roller bearings preloaded in opposition eliminate z-axis acceleration and allow for greater payloads to be tested. Using a hollow hub reduces rotational inertia providing better performance. Attaching the stinger near the center of mass of the hub reduces any induce moments that might contribute to undesired vectors of acceleration.
It is therefore an advantage of the present invention to provide a precise rotary test fixture.
It is a further advantage of the present invention to provide a larger bearing surface to control z-axis acceleration and to accommodate larger payloads.
It is a further advantage of the present invention to eliminate the variability of the force exerted on the rotary testing device by utilizing the precise control available with a shaker/controller system.
Still other advantages of the present invention will be readily apparent to those skilled in the art from the following detailed description, wherein I have shown and described the preferred embodiment by way of illustration of the best mode of the invention. Where appropriate, other embodiments have been discussed, however, still further alternative embodiments may be made without departing from the invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature and not as restrictive.